This proposal describes a project to characterize genetic exchange in Bartonella mediated by a bacteriophage-like particle. The increased incidence of pathogenic or antibiotic-resistant strains of bacteria poses a significant health threat to humans. Horizontal transfer of genes encoding virulence determinants and resistance markers is the primary mechanism for this emergence. Gene transfer is mediated by bacterial conjugation, transduction via bacteriophages, or natural transformation. A variety of unrelated bacterial species within the Bartonella, Bacillus and Serpulina genera possess remarkably similar bacteriophage-like particles (BLPs), that randomly package genomic sequences from their bacterial host. The Principal Investigator hypothesizes that BLPs participate in intraspecies, and possibly interspecies, exchange of genetic material by Bartonella. To address this hypothesis, the investigators propose to use Bartonella species as a model for characterizing BLP-mediated gene transfer. Transduction will be monitored by the transfer of antibiotic resistance from donor strains that have been mutated by allelic exchange, to host strains of Bartonella. Intraspecies and interspecies transduction will be done using both pathogenic and non-pathogenic Bartonella species, with the hope of establishing whether BLPs exhibit a host range. Transduction will be done by incubating purified phage, or a BLP donor strain, together with a host strain. In addition, an attempt to transduce virulence determinants between Bartonella species will be made. The final goal of the proposed research is to initiate a genetic analysis of the BLP genome to better understand the mechanism of phage replication and DNA packaging, with the hope of eventually harnessing the BLP for phagemid production and genetic manipulation of Bartonella. The proposed research will generate valuable insight into a genetic exchange mechanism in a group of important human pathogens, possibly provide clues regarding the emergence of five Bartonella species.